Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$79.97	13.456%	$90.7308	$90.73	$90.75	$90.70
Purchase #2	$34.80	7.276%	$37.332	$37.33	$37.35	$37.30
Purchase #3	$150.68	9.441%	$164.9057	$164.91	$164.90	$164.90
Purchase #4	$81.50	5.315%	$85.8317	$85.83	$85.85	$85.80
Purchase #5	$11.28	11.238%	$12.5476	$12.55	$12.55	$12.50
Purchase #6	$118.51	9.298%	$129.5291	$129.53	$129.55	$129.50
Purchase #7	$226.50	5.107%	$238.0674	$238.07	$238.05	$238.10
7 purchase totals =	$703.24		$758.9443	$758.95	$759.00	$758.80